278 NATURAL SCIENCE. Oct., 



important, but usually much neglected, subject of crystal twinning is 

 adequately treated, and a good description is given of the rather 

 human property of crystalline mimicry, by virtue of which crystals so 

 frequently pretend to higher symmetry than they really possess. 

 Considerable space is devoted to the methods of crystal calculation, 

 but no reference is made to the important applications v/hich the 

 method of least squares has received in this connection at the hands 

 of Beckenkamp, Hecht, and others. 



Many of the specific instances which abound in the volume are 

 of specimens preserved at the British Museum (Natural History) at 

 South Kensington. Professor IMaskelyne's volume will consequently 

 commend itself as an agreeable companion to the provincial geologist 

 or mineralogist while holiday-making in London. 



W. J. Pope. 



An Introduction to Chemical Crystallography. By Andreas Fock, Ph.D. 

 Translated and edited by William J. Pope, with a preface by N. Story- 

 Maskelyne, M.A., F.R.S. Royal 8vo. Pp. 189. Price 5s. 



Crystallography has been such a valuable aid to the study of 

 minerals that it has almost come to be regarded as an integral 

 portion of the science of mineralogy. That this is not the case, 

 however, is sufficiently proved by the fact that many of the numerous 

 products of the chemical laboratory crystallise in forms never met 

 with in minerals. Hence, crystallography would not be complete 

 unless these were included. 



The editor of this little work (Mr. W. J. Pope), in preparing the 

 present edition, has been actuated by the desire to make clear to 

 English chemists the great importance of a knowledge of crystallo- 

 graphy to their science, it having become generally recognised during 

 the past few years that the most important advances in crystallo- 

 graphy are to be expected from the chemical side. Despite the fact 

 that our knowledge of the physical and geometrical properties of 

 crystals is now very complete, their relations to chemical constitution 

 and composition are as yet but little known, although the study of 

 these characters by mathematicians and mineralogists has yielded 

 results which affect some of the highest problems in chemistry. The 

 examination of new crystalline compounds with the aid of a polarising 

 microscope can be accomplished almost as rapidly as the determina- 

 tion of the melting point, and should certainly supplement the latter ; 

 inasmuch as such an examination affords an infallible test of the 

 identity or non-identity of two substances. 



It frequently happens that translators of German scientific works 

 adhere too strictly to the idiom of the original language, and write 

 sentences which are extremely involved and difficult to follow. This 

 cannot be said of the work under discussion. The language used is 

 so clear that it reads in every way as an original production. If, 

 however, the book is compared with the German edition it is found 

 that many modifications have been made in the text and numerous 

 additions, so that it is brought up to the present day. These, we are 

 told, have been done with the author's sanction. The matter is 

 arranged in excellent sequence, and the propositions are logically 

 argued out. The book is very free from typographical errors. 



A perusal of the book can leave no doubt in the reader's mind 

 that Mr. Pope has attained his object. The close connection of 

 crystallography with other branches of physical chemistry is clearly 



